Method of mounting a transducer to a driveshaft

ABSTRACT

A method of mounting a transducer to a driveshaft which eliminates the need for a transducer housing, the improved method directly attaches the transducer to a rigid distal tip of a driveshaft which is part of a rotatable imaging core of a catheter assembly. The method contemplates heat treating the distal tip of the driveshaft to make it rigid, machining the distal tip to be dimensioned to hold the transducer, and attaching the transducer to the distal tip by clamping, crimping, or an adhesive.

PRIOR APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 09/755,873, filed on Jan. 4, 2001.

FIELD OF THE INVENTION

The present invention relates, in general, to transducer mountings forultrasound catheter assemblies used in diagnostic or therapeuticapplications.

DISCUSSION OF RELATED ART

Mechanically scanned ultrasound catheter assemblies employ a singletransducer mounted inside a rotating housing. In particular, thetransducer transmits and receives ultrasonic waves while the transducerhousing rotates about a fixed axis in an acoustic window located at adistal tip of the catheter. The rotational motion of the transducerhousing is accomplished by a flexible driveshaft that extends through anaxially disposed lumen of the catheter, wherein the driveshaft has oneend connected to the transducer housing. Once the distal end of thecatheter is positioned, for example, in a patient's vascular system, across-sectional image of the tissue surrounding the distal catheter tipis produced by using imaging and control circuitry that are electricallycoupled to the transducer via an electrical conductor extending throughthe drive shaft.

With respect to FIG. 1, a conventional prior art ultrasound catheterassembly 100, which appears in U.S. Pat. No. 5,842,994, is depicted.U.S. Pat. No. 5,842,994 is hereby incorporated by reference. Thecatheter assembly 100 comprises a first elongate tubular element 120,which forms an axially disposed lumen 130. An acoustic imaging window140 is attached to a distal end of the first tubular element 120,thereby forming an enclosed tip of the catheter assembly 100. A flexibledriveshaft 150 extends through the lumen 130 and is connected at adistal end to a transducer housing 60 disposed in the acoustic imagingwindow 140. The transducer housing 60 has a generally cylindricaltransducer 170 mounted therein, exposing a circular active surface area,or aperture. A second elongate tubular element 180 forms an additionallumen 190 used for other catheter functions such as housing pullwires ordelivering liquid to a distally disposed balloon during angioplasty.

With further reference to FIG. 1, the transducer housing 60 is anexpensive, high-precision part that requires a particular joiningoperation to attach it to the driveshaft 150. In addition, the jointcreated between the driveshaft 150 and the transducer housing 60 maypotentially fail. Therefore, it would be advantageous to eliminate thetransducer housing 60 from catheter assembly 100. FIG. 1A depicts analternative conventional prior art ultrasound catheter, which includesopening 65 adapted to permit flushing from the proximal end of catheterassembly 100 and, if a separate lumen is provided, dimensioned for thepassage of guide wires. This alternative catheter does not include firstelongate tubular element 120 or second elongate tubular element 180.

SUMMARY OF THE INVENTION

An aspect of the invention involves a method of making a transducermounting to a driveshaft by providing an elongate tubular elementincluding a lumen, providing a rotatable imaging core adapted to passthrough the lumen, the imaging core including a flexible driveshaft anda transducer. The method optionally contemplates treating and machiningthe distal tip of the driveshaft, and then attaching the transducer tothe distal tip.

Another separate aspect of the invention involves a method of making atransducer mounting to a driveshaft comprising a step of treating thedistal tip of the driveshaft by hardening the distal tip with a weldingprocess, wherein the driveshaft is initially made of flexible woundwires and the welding process joins the wound wires of the distal tiptogether such that a rigid distal tip is formed. This method optionallycontemplates the use of electrical welding by applying electrodes at twolocations on the drive shaft for electrical conductivity therebetween.

A further separate aspect of the invention involves a method of making atransducer mounting to a driveshaft comprising a step of treating thedistal tip of the driveshaft by hardening the distal tip with asoldering process, wherein the driveshaft is made of flexible woundwires having interstices therebetween and the soldering process fillsthe interstitial spaces such that a rigid distal tip is formed. Thismethod optionally contemplates the use of a cold clamp having a highspecific heat to dissipate excess heat during soldering. In addition,this method may incorporate the use of a ceramic or fiber-optic plug forkeeping the central lumen open during soldering.

An additional separate aspect of the invention involves a method ofmaking a transducer mounting to a driveshaft comprising a step ofmachining the distal tip of the driveshaft by grinding or drilling thedistal tip to form an arcuate recession with opposing tapered sidewalls. This method optionally contemplates attaching the transducer tothe distal tip of the driveshaft by crimping the tapered side wallsabout the perimeter of the transducer so that the transducer is held inplace therebetween. In addition, a clamping member or an adhesive may beused to secure the transducer to the distal tip of the drive shaft.

Yet another separate aspect of the invention involves an ultrasonicimaging catheter assembly comprising an elongate tubular elementincluding a lumen, a rotatable imaging core adapted to pass through thelumen, the rotatable imaging core including a flexible driveshaftattached to a transducer, wherein the driveshaft has a rigid distal tipadapted to be mounted to the transducer.

An additional separate aspect of the invention involves an ultrasonicimaging catheter assembly having a driveshaft with a rigid distal tipwhich includes an arcuate recession with opposing tapered side walls,wherein the transducer is attached to the distal tip of the driveshaftby crimping the tapered side walls about the perimeter of the transducerso that the transducer is held in place therebetween. Alternatively, aclamping member or an adhesive may be used to secure the transducer tothe distal tip of the drive shaft.

The invention may include any one of these separate aspectsindividually, or any combination of these separate aspects.

Other features and advantages of the invention will be evident fromreading the following detailed description, which is intended toillustrate, but not limit, the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention, in which similar elements are referred to bycommon reference numerals.

FIG. 1 is a cut-away partial side view of a prior art ultrasoundcatheter assembly.

FIG. 1A is a cut-away partial side view of a prior art ultrasoundcatheter assembly.

FIG. 2 is a cut-away partial side view of an ultrasound catheterassembly according to an example embodiment of the present invention.

FIG. 2A is a cross-sectional view taken along line 2A-2A of FIG. 2.

FIG. 3 is a cut-away partial side view of the ultrasound catheterassembly of FIG. 2.

FIG. 3A is a cross-sectional view taken along line 3A-3A of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With respect to FIGS. 2 and 3, a preferred ultrasound catheter assembly100 includes an elongate tubular element 115 having tubular section 120,which forms an axially disposed lumen 130. A dome-shaped acousticimaging window 140 is attached to a distal end of the elongate tubularelement 115, thereby forming an enclosed tip of the catheter assembly100. Alternatively, the shape of the acoustic imaging window 140 may bevirtually any shape or combination of shapes. An imaging core 145comprising a flexible driveshaft 150 having a rigid distal tip 160 and agenerally cylindrical transducer 170 is disposed within lumen 130. Theimaging core 145 is capable of translation along its center axis 185.

As best seen in FIG. 2A, axially disposed lumen 130 has a substantially“D-shaped” cross-section wherein the inner dimensions of lumen 130 aresufficient for transducer 170 to be translated therein. With furtherreference to FIG. 2A, a solid section 180 of elongate tubular element115 forms an additional lumen 190 used for other catheter functions suchas, by way of non-limiting examples, housing pullwires, drug delivery,balloon angioplasty, laser ablation, or for housing a stiffening memberto help prevent the collapsing of the catheter assembly.

A cover tube 200 formed of a suitable material, such as a heatshrinkable nylon, urethane, polyethylene or other plastic, is disposedaround tubular element 115, wherein cover tube 200 provides bothstructural integrity to the catheter assembly 100, as well as a smoothouter surface for ease in axial movement in a patient's body passagewith minimal friction. Preferably, the acoustic imaging window 140 hasits proximal end open and its distal end rounded and is attached to adistal outer circumferential portion of the tubular element 115 to forman enclosed catheter tip 210, with respective ends of the cover tube 200and acoustic imaging window 140 bonded together at a common joint 220.The outer diameter of the proximal end of window 140 is preferablysubstantially equal to that of the installed cover tube 200, so that asmooth outer surface is provided at joint 220.

Referring to FIGS. 2 and 3, the transducer 170 is attached to theflexible driveshaft 150 at a cut-away portion 165 of rigid distal tip160 such that its active surface 175 slopes at a slight angle withrespect to the center axis 185 of driveshaft 150. This tilting oftransducer 170 helps to minimize internal reflections inside of cathetertip 210. The transducer 170 can be fixedly attached in a number of waysincluding by an adhesive such as a UV (ultraviolet light) cure epoxy, bycrimping of opposing tapered side walls 195 surrounding cut-away portion165, by a clamp 205, any other known method of affixing, or anycombination of these methods.

As best seen in FIGS. 3 and 3A, driveshaft 150 has a central lumen 225adapted for the passage of transducer wires or coaxial cable, whichextend through relieved area 163. The driveshaft 150 is made of woundwire such as a super alloy or stainless steel in order to be flexibleinside of a patient's blood vessel, for example. However, distal tip 160of driveshaft 150 preferably should be hardened and machined in order tomount transducer 170. Hardening of distal tip 160 can be accomplished bya number of means including welding and soldering.

Welding of the distal tip 160 is preferably accomplished electrically,by applying electrodes at two locations along distal tip 160 forconductivity therebetween. The two locations can be the end of distaltip 160 and, for example, location 230 along the driveshaft 150. Byrunning sufficient electricity between these two locations, the woundwires of driveshaft 150 will heat up, begin to liquefy, and bondtogether, eliminating some of the interstitial spaces between the woundwires. Although electrical welding of the distal tip 160 should becontinued until the wires have fused together, it should be terminatedbefore unwanted deformation of the distal tip 160 has occurred. Afterwelding and a brief cool-down period, the distal tip 160 will be morerigid than the rest of the driveshaft 150 due to the fusing between thewound wires.

Alternatively, the hardening of the distal tip 160 can be accomplishedby a soldering process wherein the interstitial spaces between the woundwires are filled with softened metal. Although many different solderscan be used, the solder is preferably a 5% silver solder mixed with 95%tin. During the soldering process, the silver solder should be heated toapproximately 850-900 degrees Fahrenheit and melted into theinterstitial spaces in the distal tip 160 of driveshaft 150.Alternatively, a brazing process can be used, which requires greatertemperatures to melt solder having a higher percentage of silver.

During soldering, a cold clamp can be utilized to dissipate excess heatand to limit unnecessary fusion of the wound wires of the rest of theflexible driveshaft 150. Ideally, the cold clamp is made of metal suchas aluminum or copper having a high specific heat. Also, the cold clampis circular so that it can encircle the perimeter of drive shaft 150 atlocation 230. Before soldering, a plug should be inserted within centrallumen 225 so that it is not stopped up by melted metal. Preferably, theplug is made of a material having a high melting point such as a ceramicrod or a piece of fiber optic. In addition, the plug can have an outercoating to prevent adherence to the solder.

The hardening of the distal tip may also be accomplished using anadhesive such as an epoxy wherein an adhesive is used to fill theinterstitial spaces of the wound wire of distal tip 160. After thedistal tip 160 has been hardened so that it is rigid, it can be machinedto create an effective mount for transducer 170.

During machining, a cut-away portion 165 in the form of an arcuaterecession with opposing tapered side walls 195 is formed on the rigiddistal tip 160 using a milling or grinding process. In addition,relieved area 163 is formed within cut-away portion 165 using a similarmilling or grinding process. Cut-away portion 165 is adapted to receivethe cylindrical transducer 170. The opposing tapered walls 195 ofmachined distal tip 160 can be crimped inwardly about the perimeter ofthe transducer 170 to hold it fixedly in place. Additionally, an epoxyor other adhesive such as a UV cure epoxy can be used to further securetransducer 170 to distal tip 160. Alternatively, clamping member 205 canbe used to secure the transducer 170 to the distal tip 160 of thedriveshaft 150. The clamping member is fixedly attached to thedriveshaft 150 and removably attached to the transducer 170.

Any one or more of the features depicted in FIGS. 1-3, or described inthe accompanying text, may be interchanged with that of another figureto form still other embodiments.

While preferred embodiments and methods have been shown and described,it will be apparent to one of ordinary skill in the art that numerousalterations may be made without departing from the spirit or scope ofthe invention. Therefore, the invention is riot limited except inaccordance with the following claims.

1. An ultrasonic imaging catheter assembly comprising: an elongatetubular element including a lumen; a rotatable imaging core adapted topass through the lumen, the rotatable imaging core including a flexibledriveshaft, the driveshaft comprising a plurality of wires woundtogether and having interstices therebetween, the wires forming a rigiddistal tip machined such that a transducer is attachable thereon; andthe transducer attached to the driveshaft.
 2. The ultrasonic imagingcatheter assembly of claim 1 wherein the wires in the rigid distal tipare joined together.
 3. The ultrasonic imaging catheter assembly ofclaim 1 further comprising a softened metal located in the intersticesof the rigid distal tip.
 4. The ultrasonic imaging catheter assembly ofclaim 1 further comprising an adhesive located in the interstices of therigid distal tip.
 5. The ultrasonic imaging catheter assembly of claim 1wherein the rigid distal tip comprises crimped side walls about theperimeter of the transducer, wherein the crimped side-walls hold thetransducer therebetween.
 6. The ultrasonic imaging catheter assembly ofclaim 1 wherein the transducer is removably attached to the driveshaftwith a clamping member.
 7. The ultrasonic imaging catheter assembly ofclaim 1 wherein the transducer is attached to the distal tip with anadhesive.
 8. The ultrasonic imaging catheter assembly of claim 1 furthercomprising a generally cylindrical imaging window.
 9. The ultrasonicimaging catheter assembly of claim 1 wherein the transducer has acircular surface.
 10. The ultrasonic imaging catheter assembly of claim1 wherein the elongate tubular element further includes a second lumen.11. The ultrasonic imaging catheter assembly of claim 10 wherein thesecond lumen is adapted to house a steering pullwire.
 12. A catheterassembly comprising: an elongate tubular element including a lumen; arotatable imaging core adapted to pass through the lumen, the rotatableimaging core including a flexible driveshaft having a distal tip; andthe flexible driveshaft comprising a plurality of wires wound togetherand having interstices therebetween, wherein at least one interstice atthe distal tip is filled with solder.
 13. The catheter assembly of claim12 further comprising a cold clamp clamped to the driveshaft, the coldclamp having a high specific heat.
 14. The assembly of claim of claim 13wherein the cold clamp is made of aluminum.
 15. The catheter assembly ofclaim 13 wherein the cold clamp is made of copper.
 16. The catheterassembly of claim 12 wherein the wires define a second lumen locatedwithin the driveshaft.
 17. The catheter assembly of claim 16 furthercomprising a plug located within the second lumen to prevent solder inthe distal tip from plugging the second lumen.
 18. The catheter assemblyof claim 17 wherein the plug is ceramic.
 19. The catheter-assembly ofclaim 17 wherein the plug includes a piece of fiber-optic.
 20. Thecatheter assembly of claim 12 wherein the elongate tubular elementfurther includes a third lumen.
 21. The catheter assembly of claim 20Wherein the third lumen is adapted to house a steering pullwire.